The best known of Soviet SF writers, the Strugatsky brothers (Hard to Be a God, etc.) in this novel envision a future world communist state whose Progressors travel to other stars to give less advanced aliens aid and guidance they never requestedbut cannot refuse. Problems crop up at home, though, when Maxim Kammerer, head of the Department of Unusual Events, finds a rapid increase of unexplained phenomena: mass phobias, sightings of monsters, the sudden transformation of ordinary people into geniuses. The only theory that begins to cover these oddities is that of the Wanderers, a hypothetical supercivilization manipulating Earth. The tension of a bureaucracy fraying as it vainly tries to quantify the ineffable occasionally recalls the work of Stanislaw Lem, but aside from its interesting comment on Soviet imperialism, this is a sturdy if unexceptional effort. (April)